Got a test tonight, online, need help with factoring polynomials...?

Question

I haven't done this in a while... Could someone please show me the steps or help me out a little... Thanks...

3x^2 - 8x -11

I know the answer is (3x - 11)(x +1)

Just dont know how to get it

Answer 1

You know the factors must look something like this:
(3x +/- ?)(x -/+ ?)
The only way to get11 is 11*1, and since the 11 is negative, either 11 is negative or 1 is negative, but not both.
So we have :
(3x +/- 11) (x-/+1)
The middle term has to be -8x so think a little and get
(3x-11)(x+1)